The present invention relates to a hybrid electric vehicle having an electric motor and an internal combustion engine and a method of control thereof. More particularly, the present invention provides a post-transmission, parallel hybrid electric vehicle wherein the motor provides torque fill directly to a drive axle via a differential when the engine is torsionally isolated from the differential due to a shift in the transmission.
The primary objective of the automobile industry is the development of safe vehicles for personal mobility that meet or exceed customer expectations for performance, including acceleration, braking, maneuverability, and comfort, while minimizing the impact on the environment.
The automobile is an integration of many complex nonlinear systems, one of which is the powertrain system. The vehicle powertrain is a composition of electrical, mechanical, chemical, and thermodynamic devices connected as a nonlinear dynamic integrated system, with the primary objective of providing the power source for transportation. A conventional vehicle powertrain consists of an internal combustion engine (ICE), transmission, and driveline including a differential and axle system with drive wheels. An electric vehicle (EV) powertrain consists of an electric motor, gearing, and driveline including a differential and axle system with drive wheels. Also included are accessories and peripherals connected to the powerplant such as power steering, power brakes, and air conditioning.
Combining an EV powertrain system with conventional powertrain components results in a hybrid electric vehicle (HEV). A parallel hybrid electric vehicle (PHEV) configuration consists of an electric motor powertrain system and a conventional powertrain system that can provide tractive power to the drive wheels simultaneously. A PHEV can be synthesized using a conventional spark-ignited or combustion-ignited ICE powerplant/alternator combination, combined with a transmission/differential and with an ac-induction traction motor attached after the differential.
The HEV is motivated by the limitations of batteries contained in the EV, for providing extended range and performance. Including an auxiliary powerplant, such as an ICE/alternator combination, along with a conventional EV powertrain, can potentially extend the vehicle performance envelope and fuel economy, while mitigating the effect of emissions over a conventional ICE powertrain.
Most conventional ICE-powered vehicles that have an automatic transmission have a planetary gear-type transmission. In the planetary gear-type transmission, most of the gears revolve about a common axis. At the front end of the transmission is a torque converter. The torque converter provides a fluid turbine torque transfer arrangement providing a smooth gear shift. However, the torque converter on the conventional automatic transmission induces parasitic losses in the driveline.
Most manual transmissions are layshaft-type transmissions. The layshaft transmission has a dry clutch between itself and the engine. Selectively clutched gears on the layshaft are manually selected for engagement with the output shaft to provide the desired gear ratio.
In the early attempts approximately one-half century ago to provide for automatic transmissions, efforts were made to use layshaft transmissions wherein an electric motor would shift the transmission in lieu of operator input. Such transmissions were typically referred to as automated manual transmissions.
HEVs have an inherent cost disadvantage over internal combustion powered engines or EV powered engines in that they require the capital cost of two power plants. It is highly desirable that maximum efficiencies in fuel economy be obtained to make such vehicles more receptive to the buying public.
Accordingly, many HEV designs have an automated manual transmission. During shifting of an HEV automated shift manual transmission, when the engine or engine and motor in combination powers the vehicle, torque to the drive wheels is disrupted or reduced. This torque disruption can severely affect driveability, degrading the perceived quality of the vehicle. The affect on driveability is related to the change in acceleration that occurs when torque is removed or reduced from the drive wheels due to engine clutch engagement and disengagement. Both torque magnitude and frequency changes can be felt by the driver, thus affecting driveability.
Therefore it is desirable to allow the motor to add torque during transmission gear changes in a manner that is imperceptible to the vehicle operator. These and other issues related to hybrid electric vehicles are the subjects of U.S. Pat. Nos. 4,533,011; 5,337,848; 5,669,842; 5,755,302; and 6,019,698.
Although some of the aforementioned patents reveal HEVs wherein the electric motor can contribute torque to the transmission when an engine clutch is disengaged during a transmission shift, these patents require that the motor contribute torque to a drive axle of the vehicle via the transmission. Accordingly, the motor must not only contribute torque to the drive axle but also contribute torque to portions of the transmission. It is preferable that the motor be directly coupled to the drive axle or be directly coupled to the drive axle by its own clutch so that there is minimal loss of torque from the motor to the drive axle.
Minimizing torque loss from the motor to the drive axle can result in an advantage of a smaller motor providing enhanced torque output performance characteristics to the vehicle. The enhanced torque output provides greater vehicle acceleration.
It is desirable to provide a post-transmission, PHEV arrangement and method of control thereof wherein a manual automated transmission with a dry clutch can be utilized to maximize fuel economy, while at the same time being operated in a manner to minimize vibration and reaction during gear changes of the transmission.
It is also desirable to provide a PHEV as described above and a method of operation thereof that can be quickly modified for utilization with a selection of manual automated transmissions having different synchronizing and control schemes.
The vehicle driveline of the present invention accepts ICE torque and electric motor torque (in a regenerative or motoring mode), and delivers torque to the wheels through a differential and halfshafts. Motor torque is delivered via a transaxle and differential to a halfshaft. Motor torque is summed with engine torque at the differential. The engine is connected directly to the differential through an engine clutch, transmission and final drive (a propshaft if applicable), as in a conventional powertrain.
The driveline includes an automated manual layshaft transmission that lies between the engine clutch and the differential. A controller commands the motor to provide torque to the drive wheels during transmission shifting in a seamless manner, improving driveability.
The control system provides digital filtering that is activated during engine clutch disengagement and engagement. Different filters and control logic are used for clutch disengagement from full engagement to the touchpoint, disengagement from the touchpoint to full disengagement, engagement from full disengagement to the touchpoint and engagement from the touchpoint to full engagement. Different filters and control logic are used depending upon the selected transmission gear and the state of engine clutch engagement and disengagement. In lower gear, more torque is transmitted through the driveline so longer filter time constants are utilized to maintain good driver feel.
It is an advantage of the present invention to free a post-transmission HEV to have the enhanced fuel economy afforded by automated manual transmissions by providing torque transfer to the drive axle from the motor in a more continuous smooth fashion.